Non-Visualized organs at 20 Week Ultrasound

I had my 20 week ultrasound yesterday. Everything looked great. The baby is even measuring a week ahead of his due date. Except...the ultrasound tech asked me to come back in 4 weeks because she couldn't visualize the stomach. 
She found all other organs including the kidneys and bladder which was full during the ultrasound. My cute little boy was even seen drinking on the Ultrasound. The ultrasound tech told me that it is completely normal to not be able to see the stomach at the 20 week ultrasound because it has to be full to be seen. She tried to reassure me to not worry, but it's difficult to not. My husband also isn't worried. 
I just wanted to throw out there and see if this has happened to anyone and what the outcome was? Thank you for sharing!